Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $182.96   13.719%   $208.0603   $208.06   $208.05   $208.10  
  Purchase #2 $49.33   10.171%   $54.3474   $54.35   $54.35   $54.30  
  Purchase #3 $209.66   5.706%   $221.6232   $221.62   $221.60   $221.60  
  Purchase #4 $152.67   7.506%   $164.1294   $164.13   $164.15   $164.10  
  Purchase #5 $56.96   11.218%   $63.3498   $63.35   $63.35   $63.30  
  Purchase #6 $142.52   6.362%   $151.5871   $151.59   $151.60   $151.60  
  Purchase #7 $246.92   10.438%   $272.6935   $272.69   $272.70   $272.70  
  7 purchase totals = $1,041.02       $1,135.7907   $1,135.79   $1,135.80   $1,135.70